New World monkeys are limited to tropical
forest environments of southern Mexico, Central, and South America. All of
these monkeys are
predominantly arboreal and
mostly herbivorous.
They eat leaves, fruits, nuts, gums, and occasional small
prey such as insects. Today, there are at least 53 species
commonly divided into two families--Cebidae
andCallitricidae .

Cotton-top tamarin

Pygmy marmoset

The Callitricidae
consist of marmosets
and tamarins.
They range in weight from only 5 to 32 oz. (140-900 g.), but their thick fur and long
tails deceptively make them look larger and heavier.
The marmosets are the
smallest of all monkey species.Both
marmosets and tamarins are considered to be the most primitive monkeys
because of their anatomical and reproductive characteristics. Their thumbs are not
opposable. They have claws on all digits except for their big toes, which
have nails. They do not have prehensile tails.
They also lack the ability to change their facial expressions. Twin births are
common. All other primate species usually give birth
to only one child at a time. In addition,
marmoset and tamarin infants are usually carried on their father's back and
are generally only passed over to their mother for nursing.
Apparently, marmosets are unable to maintain a very stable
core body temperature.
It can vary as much as 8.5º F. (4º C.) over a day. Fortunately for
them, they live in warm forest environments that fluctuate little in
temperature.

The favorite food of tamarins and marmosets is carbohydrate rich tree sap which they tap by gnawing
holes in trunks. Their territories are centered on the trees that they
regularly exploit in this way. Some tamarin species eat flower nectar as
well. The smaller marmosets venture into
the very top of forest canopies to hunt insects that are abundant there.

Most of the
New World monkeys are in the family
Cebidae which is commonly subdivided into
four subfamilies:

1.

Cebinae(squirrel and capuchin
monkeys)

2.

Aotinae(night and titi
monkeys)

3.

Atelinae(howler and spider monkeys)

4.

Pithecinae (uakaris
and sakis)

Howler monkey

Prehensile tails
(spider
monkeys)

The Cebidaerange in weight from 1.5 to 33 pounds
(.7-14.5 kg.), which is significantly heavier than
the marmosets and tamarins. The howler
is the largest of the New World monkeys. Like
the indris of Madagascar, they have developed the unusual habit of defending territory in
the top branches of their forest canopies with vocalizations. The howlers do this
with a specialized larynx and throat that expands like a balloon. Their deep,
throaty sound is extraordinarily loud. In fact, a chorus of howler calls can carry
for several miles if the winds are favorable.

Like the Old World monkeys, theCebidaehave nails on all of their fingers and toes.Social group size varies from that of the squirrel monkey, which lives in
troops of up to 500 individuals, to that of the night (or owl) monkey, which lives in small
nuclear family groups. The
night monkey is
also notable for being the only nocturnal monkey
in the world.Unlike the prosimians, most monkeys and
all apes are diurnal.
Humans, of course, are by nature diurnal as well. Many of the
largerCebidae have strong prehensile tails that are
largely hairless on the underside and have sensitive tactile
pads. No other family of primates in either the New or the Old World
has tails
that are strong enough to function in this way as "third hands."

The Cebidaeare generally very enterprising
when it comes to obtaining food. For instance, capuchin monkeys venture
out of the trees to hunt crabs, clams, and other small animals in mangrove
swamps. They also hunt large insects and collect bird's eggs in the trees in addition to
eating leaves and fruit. Some capuchin groups collect
palm nuts, dry them out over several days, and crack them with rocks to get
at the food inside. During the rainy season when mosquitoes bother
them, capuchins rub their fur with crushed millipedes that produce a chemical
insect repellent. During the early 20th century, trained capuchin
monkeys were popular assistants for Italian organ grinders on the streets
of North American cities. In recent years, some have been trained to
be helpers for quadriplegics. Capuchins are able to do this not only
because of their typical primate manual dexterity but also because of their
relatively
high level of intelligence for monkeys. They have the largest
brain-to-body size ratio of any primate other than humans. It is not
surprising that capuchins have been observed using simple tools in getting
food. They use rocks for digging up plants as well as cracking open
seeds and smashing pieces of cacti, tubers, and lizards into bite-size
pieces. In addition, they use twigs to get insects out of small,
constricted crevices and other places.